Dec, 1916.] Relationships of Apterygotan Insects. 279 



wanting (or united with the last thoracic ganglion). Heart extend- 

 ing backward only about one third the length of the abdomen, and 

 with only two pairs of ostia. Tracheal system usually wanting, but 

 when present is best developed in Sminthurus and Sminthurides. 

 There is no anastamosing between tracheae of opposite sides of body 

 as in higher insects. The principal families of the group are the 

 Neelidse and Sminthuridse. 



Of the three groups mentioned above, the Protura are by far the 

 most primitive, and have preserved many characters which were 

 doubtless present in the ancestral insects. The Euarthrura (or 

 Entomobryid group) are rather closely related to the Protura, but 

 represent a somewhat degenerate and specialized offshoot which 

 branched off from the Proturan line at a comparatively early period 

 of development, and has become specialized in a different direction. 

 The Synarthrura (or Sminthurid group) are very closely related to 

 the Entomobryid group ; but on the whole are more highly specialized 

 than the latter. 



Styli-Bearing Apterygota (Eustyligera). 



II. Section Rhabduradclphia. 



4. Campodeoides (Rhabdura). — Styli and paired segmented 

 cerci present, but median caudal filament wanting. Mouthparts re- 

 tracted into cavity of head. Apex of mandible dentate, with a 

 dentate plate attached below it. Maxillary palpi one-segmented. 

 Antennae slender, many jointed. Eyes and postantennal organ 

 usually wanting. Transverse occipital suture distinct, and occipital 

 region comparatively large. 'Body not scaled. Abdomen composed 

 of eleven distinct segments (the eleventh being very small and 

 reduced). First abdominal segment with a pair of uropods, or 

 vestigeal abdominal legs, but no styli occur on the first segment. 

 Styli and protrusile sacs usually occur on abdominal segments two to 

 seven, inclusive. The long slender segmented cerci have no opening 

 at the tip of the terminal segment for the discharge of glands (as 

 in the Projapygidae). Anal laminae distinct. Abdominal ganglia 

 seven in number. Spiracles confined to the thoracic region (three in 

 number). Malpighian tubes represented by papillae. Ovaries simple, 

 without ovarioles. Heart with nine pairs of ostia. This order con- 

 tains the family Campodeidae. 



